The immune response after vaccination in recipients against different subtypes of tick-borne encephalitis virus (<i>Flaviviridae</i>: <i>Orthoflavivirus</i>)

Introduction. There are three antigenic subtypes of tick-borne encephalitis virus (TBEV): the European, Far Eastern and Siberian subtypes. The article discusses the topic of cross-protective neutralizing antibodies against different subtypes of TBEV. Objective ‒ the study of the immune response after vaccination against TBE in recipients immunized with Russian-made vaccines in relation to Siberian, Far Eastern, and European subtypes. Materials and methods. 100 serum samples obtained from recipients vaccinated against TBE. ELISA reagent kit was used to detect IgG antibodies to TBEV. The neutralization reaction on cell culture was used to analyze the titer of neutralizing antibodies. The following TBEV strains were used: Sofyin; Vasilchenko; Absettarov; Ekb_1887_1. Results. A decrease in the levels of neutralizing antibodies against heterologous strains compared to the vaccine strain was observed: for the Siberian strains Ekb_1887_1 and the Vasilchenko, a decrease was of 3.9 and 2.4 times, respectively; for the European strain, a 4.9-fold decrease compared to vaccine strain was observed. In case when IgG antibody titers were below 1 : 500, the titers of antibodies to TBEV strains heterologous to the vaccine did not exceed the minimum detectable value of 1 : 10. For individuals with IgG antibody titers below 1 : 100, antibodies to Sofyin strain were not detected. Individuals with reduced titers of virus-specific antibodies more often had deviations from the recommended vaccination schedule. Conclusion. Given the widespread distribution and genetic variability of the Siberian subtype, as well as the limited cross-neutralization capabilities of existing vaccines, the task of developing a combined vaccine that includes antigens of several virus subtypes seems relevant.